Catalyst containing reaction cell of powdered hydroquinone clathrated with radioactive gas



Jan. 30, 1968 D. J. CHLECK 3,366,574

CATALYST CONTAINING REACTION CELL OF POWDERED HYDROQUINONE CLATHRATEDWITH RADIOACTIVE GAS Original Filed Nov. 15, 1962 2 Sheets-Sheet 1 FLOWy 2 v 3 O REACTION K 85 GETGER TUBE 3 r CELL v MEASUREMENT PUMP AIR K,a5CLATHRATE AIR cELL READOUT FLOW 0-+o K as GEIGER TUBE CATALYZEDMEASUREMENT AIR cELL AIR CELL I4 l5 V/ READOUT PUMP 0+0 0 K 85 GEIGER'TUBE UNTREATED MEASUREMENT AIR cELL AIR CELL FIG. 2

INVENTOR.

David J. Chleck Jan. 30, 1968 D J. CHLECK 3,366,574

CATALYST CONTAINING REACTION CELL OF POWDERED HYDROQUINONE CLATHRATEDWITH RADIOACTIVE GAS Original Filed Nov. 15, 1962 2 Sheets-Sheet 2 22\/2O 23 28 /2 25 x A 0 +o' T PHOTO- PUMP MULTIPLIER OUTPUT TUBE UNTREATEDCELL 24 FIG. 3

OUTPUT PHOTO 3| 30 TUBE +0 K as O3 UNTREATED SAMPLING my; CELL 0CHAMBER? 32 GEIGER TUBE PUMP

OUTPUT IN VENTOR.

United States Patent 3,366,574 (IATALYST QONTAINING REACTIGN CELL 6FPGWDEREB HYDROQUINUNE CLATHRATED WITH RADIOACTIVE GAS David .l. Qhleclr,Dedham, Mass., assiguor, by mesne assignments, to the United States ofAmerica as represented by the Secretary of the Navy Uriginal applicationNov. 15, 1962, Ser. No. 238,064, now Patent No. 3,230,368, dated Jan.18, 1966. Divided and this application Oct. 7, 1965, Ser. No. 506,618

4 Claims. (til. 252-3011) ABSTRACT OF THE DISCLOSURE A reaction cell foruse in determining the presence and concentration of ozone in a gaseousmedium which contains hydroquinone, in powdered form, clathrated with aradioactive gas, and a catalyst which may be a silicon compound, forexample, for rapidly accelerating the decomposition of the ozone toatomic oxygen and bringing about the rapid oxidation of the hydroquinoneand the attendant release of the radioactive gas, the amount of gas soreleased being a measure of the ozone concentration.

The present application is a divisional application of applicantscopending application, Ser. No. 238,064, filed Nov. 15, 1962, now US.Patent No. 3,230,368, issued January 18, 1966.

The present invention relates generally to apparatus for and methods ofdetecting the presence and amount of an oxidizing substance in a gaseousmedium and, more particularly, to a reaction cell and systems utilizingthis cell for separating atomic oxygen and ozone and measuring theirconcentration Within a gaseous medium.

In one well-known method for measuring ozone con centration, the gasstream is bubbled through a solution of potassium iodide which isoxidized to release free iodine, and this iodine is measured bythiosulphate titration or colorimetry. Another standard method, thefluorescent one, uses either the oxidation of a fluorescent substance,such as fluorescein, to a nonfluorescent one or the oxidation of anonfluorescent substance, for example dihydroacridine, to a fluorescentone. A third method makes use of the absorption of visible orultraviolet light by ozone. One important disadvantage of this lastmethod is that the system responds to colored contaminants and dust. Amethod newer than the above three, which has increased sensitivity,depends upon the cracking of stretched rubber by the action of ozone.

None of these methods is, however, particularly suitable for field usesince they depend upon liquid absorbents, constant potential suppliesand bulky batteries.

In the May 1961 issue of Nucleonics, published by McGrawHill, there isan article entitled, Ozone Analyzer Uses Radioactive Clathrate, havingas one of its authors David I. Chleck, which describes how ozoneconcentration can be measured by running a gas stream of a Kr containingquinol clathrate and observing the amount of radioactivity released.This analyzer, which can detect ozone concentrations in the parts perten billion range or smaller has a dramatically increased sensitivityover conventional devices. Also, because it contains no solutions, it isrugged and portable.

In the September 1959 issue of Nucleonics, there is an article by theinventors entitled, Krypton in a Cage Clathrate 5 Sources, which setsforth a procedure for pro ducing radioactive clathrates of the typeemployed in the above ozone analyzer which involves crystal growth froma melt rather than from a water solution. More particularly, a sample ofquinol is placed in a pressure vessel, the

3,356,574 Patented Jan. 30, 1968 atmospheric gases are eliminated andthe apparatus then filled with carrier-free krypton containing 5% Kr.The quinol is then heated to slightly above its melting point 185 C. andthereafter slowly cooled over a long period of time. High gas pressureand controlled cooling are the factors which are employed to preventrapid crystal formation. The maximum clathrating efliciency obtainedwith the above process occurred at sixty atmospheres and over aseventy-two-hour growth period. Clathrate compounds prepared by theabove method contained about 25% of the theoretical maximum of krypton.

The quinol-Kr clathrate thus prepared, as mentioned hereinbefore, may beused in a sensing cell to detect and measure those nonradioactivecompounds which are capable of oxidizing the clathrate and releasing theradioactive krypton. For example, ozone oxidizes quinol t0 quinone toliberate the krypton as follows:

Since radioactivity determinations are far more sensitive and easier tomake than similar level determinations dependent on physical andchemical changes, the ozone analyzing apparatus of the above article hasa greater sensitivity and structural simplicity than prior art devices.

In atmospheric research, it is oftentimes important to obtain a verticaldistribution of the amount of atomic oxygen and ozone from sea level upto one hundred kilometers. The reaction cell hereinbefore described,unfortunately, does not possess either the sensitivity or speed ofresponse to operate in flight instruments. The reason for this is thatthe reaction requirements encountered in upper atmosphere research arerather extreme. For example, to give adequate speed of response foraltitude differentiation, the air stream must replace the air in ameasuring cell which is equipped with a Geiger tube at least once aminute for a balloon sonde and every few seconds for a drop sonde. Sincethe free volume in the reaction cell is usually very small, about 0.05ml., the velocity of the air through this component is extremely high. Amolecule of air is in residence in the reaction cell for only about afew milliseconds. Therefore, to achieve a high efficiency of response,the reaction must be speeded up from a few minutes to a fewmilliseconds, a change of rate of five orders of magnitude, it unreactedozone is not to come streaming out of the reaction cell.

It is accordingly a primary object of the present invention to provide amethod for increasing the rate of oxidation of organic compounds inheterogeneous gas solid reactions.

Another object of the present invention is to provide a sensing cell fordetecting ozone which has a response time in the millisecond range.

A yet still further object of the present invention is to provide amethod for preparing Kr clathrates having a high reaction efliciency.

A yet still further object of the present invention is to provide aradioactive clatluate of high specific activity which is stable overlong periods of storage and use.

A yet still further object of the present invention is to provide amethod for preparing radioactive krypton clathrate compounds havingrapid oxidation characteristics.

A still further object of the present invention is to provide a methodand apparatus for the separation of atomic oxygen and ozone based onradioactive krypton clathrates.

A still further object of the present invention is to provide an ozoneanalyzer which is flow rate independent.

A yet still further object of the present invention is to provide anapparatus for the separate measurement of atomic oxygen and ozoneutilizing chemiluminescence effects.

A yet still further object of the present invention is to provide anapparatus for the separate measurement of atomic oxygen and ozone basedon both clathrates and chemiluminescence.

Other objects, advantages and novel features of the invention willbecome apparent from the following detailed description of the inventionwhen considered in conjunction with the accompanying drawings wherein:

FIG. 1 is a block diagram of a system for measuring the concentration ofozone in a gaseous medium;

FIG. 2 is a block diagram of a system for measuring the concentration ofatomic oxygen and/or ozone in a gaseous medium utilizing clathratecompounds in the sensing detectors; W W 7 7 V V W FIG. 3 is analternative arrangement for measuringthe concentration of ozone and/oratomic oxygen employing chemiluminescence; and

BIG. 4 is a hybrid system for measuring and detecting ozone and/oratomic oxygen employing both clathrate compounds and chemiluminescence.

The response to ozone of the analyzer reported in the Nucleonics articleis (2) cpm=k(Conc where cpm is the counts per minute observed by theGeiger tube. This response indicates that the reaction for ozone isincomplete and yields only a few percent of what is theoreticallypossible on complete reaction with high flow rates needed foratmospheric sampling. Normally, a fractional order of reaction is commonto a gas-solid heterogeneous surface reaction. It implies a condition ofintermediate surface coverage with regard to gas molecules. Thus, thisorder of response should shift to zero or one, depending uponconcentration, if it is, in fact, caused by surface coverage. It hasbeen found, however, that the above fractional order is not due to thiscondition but to the fact that the oxidation occurs through atomicoxygen and not through the various molecular species such as 0 and 0Thus, the ozone in the gas stream undergoes slow decomposition from anequilibrium to atomic oxygen before reaction in the manner describedbelow:

gas solid complex of gas site on solid 0-5 W 1 l: s 1 To? The presentinvention in one respect thereof increases the reaction rate byaccelerating the decomposition of ozone to atomic oxygen in the reactioncell. In one particular embodiment of the present invention, a catalystin the form of calcium silicate or aluminum oxide is utilized to bringabout the above decomposition. Compounds in the silica family give ahigh reaction efficiency yet do not weaken the clathrate cage bond tothe point where the krypton gas leaks out as a result of the interactionbetween the catalyst and hydroquinone or improved oxidation due to air.

Clathrate compounds prepared in accordance with the method described inthe Nucleonics article of September 1959 are in the form of hard, fusedmasses which must be ground to a powder before they can be used in thereaction cell. This grinding process deadens reaction sites and resultsin a loss of gas at the reaction centers due to the high temperatureoxidations effected at the grinding points. Thus, the clathrate itselfhas been found to be a major source of the reaction inefiiciencypreviously mentioned.

According to one aspect of the present invention, the Kr clathrate isprepared as follows: Approximately equal volumes of a silica compoundsuch as calcium silicate and hydroquinone are placed in an inert, heavyliquid such as carbon tetrachloride. The calcium silicate, of course,precipitates to the bottom while the hydroquinone floats on top. Thismixture is then heated at the boiling point of the carbon tetrachloride.Upon complete disappearance of the organic, the mixture is decanted andallowed to dry. After drying, the powder is placed in a pressure vesseland clathrated according to the technique previously outlined. However,since the hydroquinone is absorbed into the calcium silicate, theprocess no longer results in a hard mass but in a finely dispersedpowder which can be used in the sensing cell directly. Clathratesproduced by the above method have been found to have high specificactivities of up to 1 C/grl'an'd display ex cellent stability over longperiods of storage and use. When used as ozone detectors, they displayhigh reaction efliciency and are very reproducible.

The efiiciency of the reaction cell can be improved to 100% by means ofa second catalyst, such as platinum black, added according to thefollowing procedure:

(1) A small quantity of platinum black is mixed with an inert carrier,such as sand, and boiled in carbon tetrachloride.

(2) The platinum under these conditions will coat the sand. The quantityof platinum is not critical since the sand will absorb only a finiteamount of catalysts.

(3) The mixture is decanted and dried and the excess platinum shakenoff, leaving only the coated sand.

(4) Equal volumes of this coated sand are mixed dry with the catalyzedclathrate prepared via the process previously described.

Reaction cells made of this material will provide the maximumtheoretical efiiciency at flow rates of one liter per minute withoutdeterioration in storage or use. Under these flow conditions, the halflife of the reaction is about one millisecond, improving the reactionrate by five orders of magnitude of the untreated clathrate which has ahalf life of about two minutes, as mentioned previously. The advantagesrealized with a 100% cell in the analyzer will be pointed outhereinafter.

FIG. 1 illustrates an arrangement for measuring the amount of ozone in agaseous medium which utilizes a catalyzed clathrate prepared accordingto the above described method as the reaction substance. In thisconfiguration the gaseous medium under investigation is drawn into theinstrument and placed in contact with the catalyzed clathrate reactioncell 1. The gaseous Kr which is released in an amount proportional tothe ozone concentration, is swept into the air stream and thentransported to a measuring cell 2 which contains a Geiger tube. Theoutput of this tube is registered in a conventional readout device 4.After passing through the measuring cell, the air stream is exited fromthe system by pump 3 which establishes the flow through the complexsystem.

Most gas analyzing systems of the prior art, including those employing achemiluminescent phenomenon, have an output signal which is a functionnot only of the reactant gas concentration but also of its arrival rate.In other words, the output signal is a measure of the total weight ofthe gas arriving at the sensor per unit time. Because of this flow ratedependency, precise sampling and pumping apparatus must be included inthese systems in order for the gas concentration to be accuratelydetermined.

These requirements are eliminated with the catalyzed clathrate reactioncell of the present invention as long as the system is operated at flowsno higher than that required to give 100% ozone conversion. Although thereaction cell in the system of FIG. 1 does emit krypton as a function ofthe total ozone fiux arriving thereat, the counting time within themeasuring cell is a function of the flow rate and consequentlycompensates for any variathis gas sweeps through the measuring cell atthis faster speed and is counted for a correspondingly shorter period oftime. Likewise, if the flow is slowed down, the reduced krypton iscounted for a longer period of time. The result is a signal output whichis flow rate independent, varying only in response to ozoneconcentration. This characteristic, it will be appreciated, is extremelydesirable where the apparatus is being used in a high speed, lowpressure sampling mode, such as in upper atomspheric research with sondeprobes.

From the discussion hereinbefore presented, it will be recognized thatthe hydroquinone molecule, whether or not in the form of a clathrate athigh linear flow velocities, is an inefiicient reactor with ozone and anefficient reactor with atomic oxygen arrived at directly or throughcatalyst decomposition. Specifically, if a reaction cell of hydroquinonewith a small free volume of about 0.05 ml. has air containing ozone andatomic oxygen passing therethrough at flow rates of about one liter perminute, ozone will pass therethrough 99% intact while atomic oxygen willreact completely. This difference in behavior can be employed in aciathrate instrument or in a chemiluminescent device to separate andmeasure both of these substances.

A system for measuring the ozone concentration in a gaseous mediumcontaining ozone and atomic oxygen is illustrated in block form in FIG.2. In its simplest configuration, the apparatus consists of two reactioncells, one, 19, containing a catalyzed clathrate and another, 11,containing an untreated clathrate. Both cells are subjected tosubstantial flow rates by pump 15 which, like its counterpart in FIG. 1,produces the flow of the gaseous medium throughout the system.

It will be understood from the introductory remarks that untreated cellit responds to atomic oxygen in the gas stream and not to ozone becauseof the flow rate established by pump 15. However, catalyzed clathratecell responds to both substances. Consequently, the amount of Qintroduced into measuring cell 12 is proportional to the concentrationsof the above two sub stances, while the amount of Kr sent to measuringcell 13 is proportional only to the atomic oxygen content. Hence, thedifference in Kr readings determined by these measuring cells aspresented on the readout apparatus 14 is indicative of the ozoneconcentration only. If the flow rate established by pump 15 is kept nohigher than that required for 100% conversion of the ozone in cell Itthen this system will also be flow-rate independent.

In FIG. 3 there is disclosed the general arrangement of achemiluminescent system for measuring the amount of atomic oxygen andozone in a gaseous medium. As seen in this figure, the apparatusincludes a pair of measurement chambers and 21 in a side-by-siderelationship, each being closed at one end by a chemiluminescent screen22 and at the other end, by an optical window 23. One of the intakelines, for example, the one heading to chamber 21, contains an untreatedhydroquinone reaction bed 24 for filtering out or removing atomic oxygenpassing therethrough.

The atmosphere under investigation is drawn into both chambers underflow rates of about one liter per minute and brought into intimatecontact with the chemiluminescent screen 22 by the action of pump 25which also exits this flow either around or through the screen. Becauseof the complete reaction of the atomic oxygen with the filter 24, onlyozone enters compartment 21. The half life of the atomic oxygen reactionis extremely low, for example, less than one millisecond, and at thefiow rate mentioned above, 99% of the ozone passes through filter 24without decomposition.

The ozone and atomic oxygen in compartment 20 and the ozone incompartment 21 react with the chemiluminescent material of screen 22 andproduce light in a manner well known to the art. The light signal incom- 6 partment 20, of course, has the greater intensity because of theatomic oxygen contribution.

Both measurement chambers are viewed through the optical window 23 bymeans of a rotating shutter 28 disposed in front of a conventionaldetecting photomultiplier tube 26. This rotating shutter, as is wellknown, gives the output of the photomultiplier tube as presented onoutput device 27, a square wave characteristic. The atomic oxygenconcentration, it will be appreciated, can be determined by thediiference in amplitude of the successive unidirectional wave formsmaking up the output signal.

Analyzers for measuring and differentiating atomic oxygen and ozone can,as shown above, make use of clathrates or chemiluminescents. A hybridsystem using both of these mechanisms is schematically depicted in FIG.4. Here, the air stream is drawn into an untreated clathrate cell 36which liberates Kr according to the atomic oxygen concentration thereof.The ozone in this stream passes through the cell without reactingbecause of the flow rate. The released radioactive krypton and the ozonenext enter a sampling chamber 31 which has a chemiluminescent screen 32mounted on .an inner wall portion thereof. A photomultiplier tube 33mounted on an opposite wall of the chamber views this screen and aGeiger tube 34 attached to the chamber detects the radioactive krypton.An exhaust pump 35 establishes the flow throughout the system.

It will be appreciated that Geiger tube 34 measures the amount of Krliberated by the atomic oxygen in the incoming air stream and thatphotomultiplier tube registers the amount of light produced by thereaction of ozone on screen 32. Consequently, the system of FIG. 4provides complete information as to the concentration of the atomicoxygen and the ozone in the gaseous medium under investigation.

The chemiluminescent screens employed in the modification of FIGS. 3 and4 can consist of a fluorescent dye on a suitable matrix. Typical dyesare Fluorescein, eosin, Rhodamine B, etc. Typical matrices are silicagel, silicates, paper, etc.

The hybrid system of FIG. 4 has several noteworthy advantages. First, asystem using chemiluminescents must be shielded from the light, and thisrequirement makes it ditficult to pass highly reactive atomic oxygeninto the sampling chamber. In the modification of FIG. 4, the atomicoxygen content is measured by a radioactive countmg technique, therebyavoiding the above problem. Secondly, chemiluminescence is a moresensitive and rapid indicator for ozone concentrations than clathrates.

In the system of FIG. 2 the differential reading of Geiger tubes 12 and13 is indicative of the atomic oxygen concentration. However, the ozoneconcentration can also be determined from the output of tube 13.Likewise, in the system of FIG. 3, the difference in amplitude betweenthe two square wave signals is proportional to the atomic oxygen contentbut the ozone content can be found from the amplitude of the smallersignal. In the system of FIG. 4, these concentrations are directlyavailable from the photomultiplier and Geiger tube outputs.

Gbviously many modifications and variations of the present invention arepossible in the light of the above teachings. It is therefore to beunderstood that Within the scope of the appended claims the inventionmay be practiced otherwise than as specifically described.

What is claimed is:

1. In a reaction cell for use in detecting the presence of ozone in agaseous medium and determining its concentration, the combination ofhydroquinone in powdered form clathrated with a radioactive gas; and

a catalyst for accelerating the decomposition of any ozone in saidgaseous medium to atomic oxygen to thereby bring about the rapidoxidation of said 7 8 hydroquinone and the attendant release of saidradio- References Cited active gas. P J 2. In a reaction cell of thetype set forth in claim UNITED STATES ATEL TS 1 wherein said catalystfor accelerating the decomposi- $084,062 4/1963 Chleck X tion of saidozone is calcium silicate. 5 3,230,368 1/ 1966 Chleck X 3. In a reactioncell of the type set forth in claim 1 3,299,269 1/1967 Hanson et 011 Xwherein said catalyst for accelerating the rapid decornposition of saidozone is aluminum oxide. CARL QUARFORTH, 'y Examiner- 4. In a reactioncell of the type set 'forth in claim 1, BENJAMIN R. PADGETT, Examiner.

a second catalyst consisting of platinum black for further improving theefiiciency of the reaction cell. 10 S. J. LECHERT, 511., AssistantExaminer.

